PERTH, Australia — Investigators are conducting a forensic examination of the final recorded conversation between ground control and the cockpit of Malaysia Airlines Flight 370 before it went missing three weeks ago, the Malaysian government said Tuesday. Meanwhile Australia, which is coordinating the search for the Boeing 777, cautioned that it “could drag on for a long time” and would be an arduous one.

The forensic examination could shed light on who was in control of the cockpit and will also seek to determine if there was any stress or tension in the voice of whoever was communicating with ground control — crucial factors in an air disaster investigation.

Responding to repeated media requests, the Malaysian government also released a transcript of the conversation, which showed normal exchanges from the cockpit as it requested clearance for takeoff, reported it had reached cruising altitude and left Malaysian air space.

“Good Night Malaysian three-seven-zero,” were the final words received by ground controllers at Kuala Lumpur’s international airport at 1:19 a.m. on March 8. On Monday, the government changed its account of the final voice transmission which it had earlier transcribed as “All right, good night.”

The hunt for Flight 370 has turned up no sign of the jetliner, which vanished March 8 with 239 people on board bound for Beijing from Kuala Lumpur.

The search area has shifted as experts analyzed the plane’s limited radar and satellite data, moving from the seas off Vietnam and eventually to several areas west of Australia. The current search zone is a remote 254,000-square-kilometre area roughly a 2 1/2-hour flight from Perth.

On Tuesday, Australia deployed an airborne traffic controller to prevent collisions as search planes fly over the Indian Ocean.

An Australian air force E-7A Wedgetail equipped with advanced radar was making its first operational flight, the Australian Maritime Safety Authority tweeted. Earlier, Angus Houston, who heads the joint agency coordinating the multinational search effort, said the modified Boeing 737 will monitor the increasingly crowded skies over the remote search zone.

The RAAF E-7A Wedgetail airborne early warning and control (AEW&C) aircraft is on its first operational tasking in the #MH370 search area.

On Tuesday, 11 planes and nine ships were focusing on less than half of the search zone, some 120,000 square kilometres of ocean about 2,000 kilometres west of Perth, according to the Joint Agency Coordination Center.

Low clouds, rain and choppy seas hampered search efforts Tuesday. One aircraft, a Japanese coast guard plane with high-performance radar and infrared cameras, completed just one of its three planned passes over the search area, then turned back because of the conditions. It descended to just 150 metres above the whitecaps at one point, but the crew members still couldn’t see anything out the windows.

Some of the aircraft have occasionally dipped even lower above the sea for brief periods, raising concerns of collisions with ships that are crisscrossing the zone.

Under normal circumstances, ground-based air traffic controllers use radar and other equipment to track all aircraft in their area of reach and direct planes so they are at different altitudes and distances. This enforced separation — vertical and horizontal — prevents collision. But the planes searching for Flight 370 are operating over a remote patch of ocean that is hundreds of kilometres from any air traffic controller.

The arrival of the E-7A “will assist us with de-conflicting the airspace in the search area,” Houston told reporters in Perth. The plane can survey a surface area of 400,000 square kilometres at any given time, according to the air force’s website.

Houston, a former Australian defense chief, called the search effort the most challenging one he has ever seen. The starting point for any search is the last known position of the vehicle or aircraft, he said.

“In this particular case, the last known position was a long, long way from where the aircraft appears to have gone,” he said. “It’s very complex, it’s very demanding.”

“What we really need now is to find debris, wreckage from the aircraft,” he said. “This could drag on for a long time.”

Malaysia has been criticized for its handling of the search, particularly its communications to the media and families of the passengers. In its latest misstep, the government on Monday changed its account of the final voice transmission from the cockpit.

In Tuesday’s statement, the government said that police and forensic examinations were trying to confirm if the voice belonged to the co-pilot as was earlier believed.

“There is no indication of anything abnormal in the transcript,” Malaysia’s acting Transport Minister Hishamuddin Hussein said in the statement.

Australian Prime Minister Tony Abbott has said that although the search for the aircraft has been slow, difficult and frustrating — it will continue indefinitely. In fact, he said the intensity and magnitude of operations “is increasing, not decreasing.”

“If this mystery is solvable, we will solve it,” Abbott said.

Items recovered so far were discovered to be flotsam unrelated to the Malaysian plane. Several orange-colored objects spotted by plane Sunday turned out to be fishing equipment.